Capacitor failure
Capacitor damage causes the highest number of malfunctions in electronic equipment, especially electrolytic capacitor damage is the most common. Capacitor damage manifests itself in the form of reduced capacity, complete loss of capacity, leakage, and short circuits.
Capacitors play a different role in the circuit, caused by the failure of each characteristic: in the industrial control circuit board, digital circuits account for the vast majority of capacitors are mostly used for power supply filtering, signal coupling and oscillator circuits used for less capacitance. Used in the switching power supply electrolytic capacitors, if damaged, the switching power supply may not vibrate, no voltage output;
Or the output voltage filtering is not good, the circuit due to voltage instability and the logic of chaos, manifested in the machine works well sometimes bad or can not turn on the machine, if the capacitor and in the digital circuit between the power supply positive and negative poles, the fault performance as above.
This is particularly evident in the performance of the computer motherboard, many computers with a few years on the phenomenon of sometimes can not turn on the machine, and sometimes can be turned on, open the chassis, you can often see the phenomenon of electrolytic capacitors bulging, if the capacitor will be removed to measure the capacity, and found that the actual value is much lower than the value.
Capacitor life and ambient temperature is directly related to the higher the ambient temperature, the shorter the life of the capacitor. This law applies not only to electrolytic capacitors, but also to other capacitors. So in the search for faulty capacitors should focus on checking and heat sources close to the capacitor, such as heat sinks and high-power components next to the capacitor, the closer it is, the greater the possibility of damage. So in the maintenance should focus on finding.
Some capacitors leakage is more serious, with a finger touch will even burn your hand, this capacitor must be replaced. In the maintenance of good and bad failure, excluding the possibility of poor contact, generally most of the capacitor damage caused by the failure. So when it comes to such failures, you can focus on the capacitance check, replace the capacitance is often a surprise.
Resistor failure
Often see many beginners in overhauling the circuit in the resistor on the toss, and is to tear down and welding, in fact, repair more, you just need to understand the characteristics of the damage to the resistor, there is no need to go to great lengths.
Resistors are the largest number of components in electrical equipment, but not the highest damage rate components. Resistor damage to the most common open-circuit, resistance value becomes larger less common, resistance value becomes small very rare. Commonly, there are carbon film resistors, metal film resistors, wirewound resistors and insurance resistors.
The first two types of resistors are the most widely used, and their damage is characterised by a low resistance (below 100Ω) and a high resistance (above 100kΩ) with a high damage rate, and an intermediate resistance (e.g. a few hundred ohms to tens of thousands of ohms) with very few damages; and secondly, the low resistance resistance tends to be burnt and blackened when damaged, which is easy to find, and the high resistance resistance is damaged with very few traces.
Wirewound resistors are generally used as current limiting, resistance value is not large; cylindrical wirewound resistors when burned, some will be black or surface burst skin, cracks, some have no trace; cement resistor is a kind of wirewound resistor, burned when it may break, otherwise there is no visible traces; insurance resistor burned when the surface of a piece of skin will be blown, and some do not have any traces, but will never be scorched black. According to the above characteristics, you can focus on when checking the resistor, and quickly find the damaged resistor.
According to the characteristics listed above, we can first observe the circuit board on the low resistance resistor there is no trace of burnt black, and then according to the vast majority of resistor damage or resistance value of the majority of open-circuit and the characteristics of high resistance resistance is easy to damage, we can use a multimeter in the circuit board first directly measure the resistance of the high resistance resistance of the resistance of the two sides of the resistance value.
If the measured resistance is larger than the nominal resistance, the resistor must be damaged (pay attention to wait until the resistance is stable before concluding, because the circuit may be connected in parallel with capacitive elements, there is a charge and discharge process), if the measured resistance is smaller than the nominal resistance, it is generally not necessary to pay attention to it. In this way, each resistor on the circuit board are measured once, even if the "wrong" thousand, will not let go of one.
Operational amplifier failure
Operational amplifier good or bad judgement of a considerable number of electronic repairers have a certain degree of difficulty, not only the relationship between the degree of culture, here to discuss with you, I hope to help you.
Ideal operational amplifier has a "false short" and "false break" characteristics, these two characteristics are very useful for analysing the linear use of the op amp circuit. In order to ensure linear operation, the op-amp must operate in closed loop (negative feedback). Without negative feedback, an op amp under open loop amplification becomes a comparator. If you want to judge the device, you should first distinguish whether the device is used as an amplifier or a comparator in the circuit.
According to the principle of the amplifier virtual short, that is to say, if the operational amplifier is working properly, its isotropic input and inverse input voltage must be equal, even if there is a difference is also mv level, of course, in some high-input impedance circuits, the internal resistance of the multimeter will be a little bit of influence on the voltage test, but generally will not be more than 0.2V, if there is a difference of 0.5V or more, the amplifier must be bad.
If the device is used as a comparator, it is allowed to have unequal isotropic and inverse inputs. Isotropic voltage > reverse voltage, the output voltage is close to the positive maximum; isotropic voltage.
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